This application is based on Korean Patent Application No. 1999-26942, filed on Jul. 5, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a method and apparatus that prevents a white-screen error from occurring in the LCD device, and an LCD device incorporating the method and apparatus.
2. Discussion of the Related Art
LCD devices including display and drive portions are widely adopted as a display device for notebook computers or laptop computers because of a smaller size than conventional cathode ray tubes (CRTs). And recently, as the LCD devices become to display natural-like colors, desktop computers arc also adopting the LCD device as a display device. The LCD device has advantages of low power consumption, low electromagnetic radiation, and small size compared with a CRT.
Now, with reference to FIG. 1, a detailed explanation of the drive portion of an LCD device used for a desktop computer will be provided.
An interface 10 receives horizontal synchronous signals xe2x80x9cHSYNC,xe2x80x9d vertical synchronous signals xe2x80x9cVSYNC,xe2x80x9d and image data signals xe2x80x9cDATA.xe2x80x9d The interface 10 is electrically connected (hereinafter, connected) with an interface controller 12 and an LCD controller 14, which is connected with a DC/DC converter 16. In addition, the LCD controller 14 is connected with gate-line driving circuits 18 and data-line driving circuits 20, while the gate-line driving circuits 18 and data-line driving circuits 20 are connected with gate lines and data lines of an LCD panel 22. Though not shown in FIG. 1, the LCD panel 22 has a plurality of unit pixels arranged in a matrix shape, and each unit pixel has a thin film transistor (TFT). Gate and source electrodes of the TFTs are connected by means of the gate lines and data lines with the gate-line driving circuits 18 and the data-line driving circuits 20, respectively.
From power source devices, or power supply circuits (not shown), a direct current (DC) supply voltage, for example, 3.3 VDC is applied to the DC/DC converter 16 and the LCD controller 14. Therewith, the DC/DC converter 16 provides first, second, and third output power source voltages of xe2x88x925, 16, and 8.7 VDC. Among the output power source voltages, the first and second output power source voltages xe2x88x925 and 16 VDC are supplied for the gate-line driving circuits.
As the drive portion including the interface 10 et al. receives video signals from a video card of the desktop computer, the display portion including the LCD panel 22 displays images. The role and operation of each device shown in FIG. 1 will be explained hereinafter.
When the video card transmits the video signals including HSYNC and VSYNC to the interface 10, the interface 10 processes them such that images displayed by the LCD panel 22 coincide with preset resolution and optimum display size. Herein, the interface controller 12 transmits interface control signals to the interface 10 such that the interface 10 operates according to the interface control signals. As a result, the interface 10 produces data signals which are applied to the LCD controller 14.
The LCD controller 14 transmits video data signals to the data-line driving circuits 20 according to some clock signals, and applies gate start signals and timing signals to the gate-line driving circuits 18. At this point, the DC/DC converter 16, which is supplied 3.3 VDC from the power source (not shown), provides a plurality of different DC voltage levels to the gate-line driving circuits 18 and the data-line driving circuits 20, respectively.
The data-line driving circuits 20 and the gate-line driving circuits 18 transmit pixel data and gate signals to the LCD panel 22, and the LCD panel 22 displays certain images from the pixel data signals according to the gate signals.
Hereinafter, a white screen error of the above-mentioned LCD device will be explained with reference to FIG. 2.
As shown, the LCD device conventionally has a delay time between the output power source voltages, specifically the first and second output power source voltages that are applied to the gate-line driving circuits, and the data signals that are respectively applied by the DC/DC converter 16 and the interface 10. That is to say, the output power source voltages begin to increase at a time period xe2x80x9cT1xe2x80x9d and reach their normal values at a subsequent time period xe2x80x9cT2xe2x80x9d while the data signals begin at a further subsequent time period xe2x80x9cT3.xe2x80x9d Therefore, the output power source voltages go ahead of the data signals by the time period xe2x80x9cT2,xe2x80x9d which is conventionally designed to be less than 20 ms inclusive. In other words, since there conventionally occurs an abnormal transient phase in the output power source voltages when the power source of the desktop computer is turned on or off, the output power source voltages should begin ahead of the data signals by a preset time period to assure a normal operation of the LCD device, namely, to exclude the abnormal state where the data signals are applied during the transient period xe2x80x9cT1xe2x80x9d of the output power source voltages.
However, when the delay time is too long, the output power source voltage is applied to the gate-line driving circuit too long without the display data signals being applied to the data-line driving circuit. In that abnormal case, an over-current is applied to the gate electrode of the TFT in the LCD panel such that a surge protector or breaker of the DC/DC converter powers down all of the output power source voltages. And as a result, while a back light is still illuminating, there exists no image data displayed on the LCD panel such that only a white color is shown to users, which is called as the white-screen error. The white screen error continues until the users turn off the main power for the desktop computer.
The above-mentioned problem causes users to distrust the overall product, such that repair service costs of venders are increased.
Accordingly, the principles of the present invention relate to a liquid crystal display device that is designed to substantially obviate one or more of the problems due to the limitations and disadvantages of the related art.
It is an object of the present invention to provide a method and apparatus for preventing the white-screen errors.
To achieve the above object, in one aspect the present invention provides A driving portion of a liquid crystal display device, comprising a data-line driving circuit; a gate-line driving circuit; an interface outputting data signals; a liquid crystal display controller receiving the data signals and outputting display data signals to the data-line driving circuit and timing signals to the gate-line driving circuit; a DC/DC converter supplying a plurality of output power source voltages to the gate-line driving circuit and the data-line driving circuit; a voltage detector detecting a voltage level of one of the output power source voltages supplied by the DC/DC converter and outputting a feedback signal; and an interface controller receiving the feedback signal from the voltage detector, outputting enable signals to the interface and to the DC/DC converter, and outputting a control signal to advance the data signals when the detected voltage level of the one output power source voltage is less than 90% of a preset voltage level.
Preferably, the voltage detector includes a transistor having gate, source and drain electrodes and being turned on and off according to the output power source voltage from the DC/DC converter.
Preferably, the transistor is a thin film transistor.
Also preferably, the voltage detector includes a first resistor electrically connecting the gate electrode of the transistor with an output terminal of the DC/DC converter and a second resistor electrically connecting the drain electrode of the transistor with the liquid crystal display controller, wherein the source electrode of the transistor is connected to ground, and wherein the drain electrode of the transistor is electrically connected with the interface controller.
The driving portion further includes an alarm device alerting users only when the feedback signals are abnormal in spite of outputting the data signals and the output power source voltage at the same time.
In the driving portion, the alarm device is preferably a light-emitting device emitting light according to a control signal applied from an interface controller.
Preferably, the light-emitting device includes a light-emitting diode and a resistor, wherein the light-emitting diode includes an anode electrode electrically connected with the interface controller, and a cathode electrode electrically connected with a first end of the resistor, and wherein a second end of the resistor is connected with ground.
In another aspect of the invention, a method of driving a liquid crystal display (LCD) device comprises providing a data signal for displaying an image on the liquid crystal display panel; supplying an output voltage signal used to drive the liquid crystal display panel to display the image; detecting a voltage level of the output voltage signal; providing a feedback signal indicating whether the voltage level exceeds a predetermined threshold; and in response to the feedback signal, adjusting a time interval between the output voltage signal and a start of the data signal.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. However, it should be understood that the written description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.